Smoke detectors and carbon monoxide detectors are typically mounted at various strategic locations around a house or building to detect dangerous air quality conditions as a result of such things as a fire or a smoke or carbon monoxide producing event. It is a requirement that these detector units are highly reliable so that the detector can detect conditions invisible to the human senses or problematic conditions when the occupants of the building are asleep. As such, prior detector units typically provide an indication when the battery compartment is not filled with a battery. Indeed, there are UL requirements that acceptable and reliable indications of a missing battery be provided in smoke detectors and carbon monoxide detectors.
There are various attempts in the prior art for providing missing battery indication as demonstrated by various U.S. Patents. One attempt provided by the prior art is to prevent a cover or lid from covering the battery compartment in the detector base as demonstrated by Fawcett, U.S. Pat. No. 4,881,063; Niedermeyer, U.S. Pat. No. 4,228,428; Hetherington, U.S. Pat. No. 5,820,406; Hall, U.S. Pat. No. 4,959,640 and certain embodiments of Cousins et al., U.S. Pat. No. 5,055,830. A more desirable approach is to prevent a detector base from mounting to a mounting bracket that permanently fastens to the wall. This is because there is no possibility of mounting the detector to the bracket on the wall without purposely tampering with the detector. Examples of these attempts are illustrated in Belano, U.S. Pat. No. 4,870,395 and certain embodiments of Cousins et al., U.S. Pat. No. 5,055,830.
Older smoke detectors were often powered by a single 9 volt battery. In these single battery detectors, a single lockout mechanism was provided for the battery. However, more modern detectors such as combination smoke/CO, detectors are now often powered by multiple 1.5 volt batteries because of battery life requirements. In detectors having a multiple battery compartment, multiple lockout mechanisms have been necessary to sense the presence or absence of batteries in each of the multiple individual battery receiving regions in the battery compartment because the absence of one of the batteries would be catastrophic and prevent the detector from being electrically operative. However, providing multiple lockout mechanisms is a significant disadvantage. In particular, providing multiple lockout mechanisms and assembling the same is costly. Utilizing multiple lockout mechanisms also undesirably increases complexity and occupies space.